U.S. Constitution - Article 4 Section 3

Article 4 - The States
Section 3 - New States

New States may be admitted by the Congress into this Union;
but no new States shall be formed or erected within the Jurisdiction of any other State; nor any State
be formed by the Junction of two or more States, or parts of States, without
the Consent of the Legislatures of the States concerned as well as of the
Congress.

The Congress shall have Power to dispose of and make all
needful Rules and Regulations respecting the Territory or other Property
belonging to the United States; and nothing in this Constitution shall be so
construed as to Prejudice any Claims of the United States, or of any particular
State.